Pallet racks are single or multi-level structural bulk storage systems. They support high stacking of single items or palletized loads which usually remain in the original packaging of shipping containers or boxes. Rack systems are commonly made of steel and maximize facility space while simplifying inventory tracking.

Rack load beams are typically topped with decking or cross support bars. The decking is generally made from welded wire and the cross support bars are typically cold-formed steel or structural steel members. The cross bars and decking acts as the load bearing surface. Decking sections are completely fabricated, ready-to-install decking assemblies with reinforcing members such as channels, tubes or rods that increase the rigidity and capacity rating of the assembly.

Racks can be self-supporting, standalone structures, or they can be a key component of a facility’s construction (if they are the key structural components of a building, then it is referred to as a rack supported building). These rack supported buildings use either structural rack made of hot rolled steel to support the roof and walls or cold-formed steel sections or a combination of both. The space between the racks—where personnel and load handling equipment can access the stored items—is called an aisle or storage aisle.

Whether they support the roof and walls or not, all rack systems hold heavy loads and should adhere to current local and national building codes as well current rack standards (such as RMI’s R-Mark certification. In addition, they should meet current seismic requirements) to ensure that their rated load capacity is in compliance to all applicable specifications.

There are multiple types of pallet rack, named for their type of construction or means of access. These include:

• Single deep rack - The simplest of all racking systems, it permits only one-unit-deep pallet loads to be stored side-by-side. This makes all pallets accessible from the aisle, which is why it is also called selective rack, or single deep selective rack. For greater storage density, double deep rack accommodates two pallet loads stacked back-to-back.
• Drive in rack – Ideal for storing repetitive products while maximizing cubic storage space, this structure allows a vehicle to enter from one side only to pick up or deliver pallets that rest on continuous rails. A drive in rack structure is utilized when a last-in, first-out (LIFO) inventory system is required. Similarly-constructed, drive through rack permits a vehicle to drive through the structure at any storage location along the aisle.
• Carton flow rack or flow-through rack – Ideal for small-quantity case picking, this system utilizes metal shelves equipped with rollers or wheels that allow product and materials to flow from the back of the rack to the front. Similar in concept but on a larger scale is pallet flow rack which uses conveyor wheel shelf sections that enable back-loaded pallets to flow by gravity to the front or pick face. Both carton flow and pallet flow are implemented when a first-in/first-out (FIFO) inventory system is required. Also utilizing wheels in the rack structure, push back rack allows palletized goods and materials to be stored by being pushed up a gently graded ramp. Push back, however, differs from carton flow and pallet flow in that it offers a LIFO inventory system.
• Cantilever rack - A center column-based rack with arms projecting from the columns for front-loading of large objects without obstruction from rack support uprights.
• Reel rack – Storage system specifically used to store reels of cable or cord by cradling them in the rack.
• Mobile rack or mobile sliding rack- Typically a single deep selective rack with wheels at the base for movement of the entire structure along tracks embedded in the facility’s floor.
• Portable rack – Self-contained rack units made up of bases, decks and posts available for temporary expanded storage as needed.